Which line of code should you insert at line 03?

You are developing a web page that enables customers to upload documents to a web server. The
page includes an HTML5 PROGRESS element named progressBar that displays information about the
status of the upload.
The page includes the following code. (Line numbers are included for reference only.)

An event handler must be attached to the request object to update the PROGRESS element on the
page.
You need to ensure that the status of the upload is displayed in the progress bar.
Which line of code should you insert at line 03?

A.
xhr.upload.onloadeddata =

B.
xhr.upload.onplaying =

C.
xhr.upload.onseeking =

D.
xhr.upload.onprogress =

Explanation:

Reference:
http://stackoverflow.com/questions/3352555/xhr-upload-progress-is-100-from-the-start